We have two lovely Zelkovas on our property which were planted about 8-10 years ago. They are about 10 inches in diameter and about fifteen feet tall. This spring I notice that they have bark which is peeling off of them and falling to the ground in pieces up to about 4"x10". It seems more prevalent at about 2-3 feet from the ground. They are n ot leafed out yet but they are full of buds and appear healthy other wise. Should I be worried? Any idea of what it could be? Any recommendations for care? Please advise.